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From: Cecil Westerhof <Cecil@decebal.nl>
Newsgroups: comp.lang.python
Subject: Re: Let exception fire or return None
Organization: Decebal Computing
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Date: Thu, 30 Apr 2015 16:53:43 +0200
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Op Thursday 30 Apr 2015 14:28 CEST schreef Peter Otten:

> Cecil Westerhof wrote:
>
>>> (2) you may want to take measures to limit memory usage, e. g.
>>>
>>> assert index >= 0
>>
>> I put that in, but as first statement.
>
> For the record, this was not a recommended check, but rather a way
> to communicate to the reader of my code that unlike yours it doesn't
> support negative indices.
>
>>> try:
>>> [line] = itertools.islice(f, index, index+1)
>>> except ValueError:
>>> raise IndexError
>>> return line.rstrip()
>>
>> In my case it is not important. (The biggest file I use has between
>> 100 and 200 lines), but I publish it, so I should do my best to
>> make it so lean as possible.
>
> If you keep your 
>
> return f.readlines()[index]
>
> anyway you might allow for negative indices, and then
>
> get_indexed_message(message_filename, -1)
>
> fetches the last message in the file and
>
> get_indexed_message(message_filename, slice(None, None))
>
> fetches a list with all messages.

It is even possible without keeping it. I can fetch the number of
messages and implement it myself without a possible high memory
overhead. Certainly something to think about.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof